1. Field of the Invention
The present invention generally relates to an exhaust cooling system for a marine engine and, more particularly, to a simplified system that provides cooling of exhaust gasses at a rate which is determined as a function of the operating speed of the engine.
2. Description of the Prior Art
Exhaust systems for marine propulsion devices, such as sterndrive systems, are well known to those skilled in the art. Exhaust gasses are conducted through an exhaust elbow which is cooled by a flow of a liquid coolant which is directed through passages formed in the exhaust elbow. In certain applications, the coolant passages form a water jacket around the exhaust conduit within the structure of the exhaust elbow. Many different techniques are known to those skilled in the art for managing the flow of coolant through channels associated with the exhaust system.
U.S. Pat. No. 6,290,558, which issued to Erickson on Sep. 18, 2001, discloses an exhaust elbow with a water trap for a marine propulsion system. The exhaust elbow for a marine propulsion exhaust system is provided with a water trap section that defines a water collection cavity. Within the water trap section, a barrier extends downwardly into the water collection cavity to define first and second exhaust passages. When water begins to collect in the water collection cavity, the cross sectional area of the exhaust passage is reduced and the velocity of exhaust gases passing through the exhaust passage is increased. The water collection cavity is shaped to be easily cleared when exhaust gas pressure increases as the engine speed increased.
U.S. Pat. No. 5,980,343, which issued to Rolinski on Nov. 9, 1999, describes an exhaust system for marine vessels. A two pathway exhaust and water discharge through-hull system is coupled to a muffler for separating exhaust gases and cooling water at operating speeds such that at low engine speeds exhaust gases and water are discharged through a first outlet preferable above the waterline and, when the engine speed is increased above a predetermined level, exhaust gases are discharged through a second outlet which communications with a streamlined, low back-pressure underwater discharge skeg and water is discharged through the first outlet.
U.S. Pat. No. 5,421,756, which issued to Hayasaka on Jun. 6, 1995, describes an exhaust system for a marine propulsion machine. An exhaust gas discharge system is provided for a watercraft. The system has a first discharge path, including a first outlet, primarily for use during high speed vessel operation and a second discharge path, including a second outlet, for use during both low and high speed vessel operation. The first outlet is arranged to constantly remain below a water surface level of a body of water within which the watercraft is operated, while the second outlet is arranged to locate above the water level surface during high speed vessel operation and to located below the body of water, at a level higher than the first outlet, during idle and low speed vessel operation.
U.S. Pat. No. 4,831,822, which issued to Yoshimura on May 23, 1989, describes an exhaust system for a marine engine. The exhaust system has an exhaust conduit into which the exhaust gases and engine coolant are discharged. The exhaust conduit has a separator portion that is affected to separate the coolant from the exhaust gases under high speed running conditions so as to achieve maximum power output through a reduction in back pressure but substantially no separation is provided at low speeds so that silencing will not be adversely affected.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
An exhaust system for a marine engine, made in conformance with the preferred embodiment of the present invention, comprises an exhaust conduit, a coolant conduit, a coolant inlet port, and an orifice. The exhaust conduit is shaped to be connected in fluid communication with at least one exhaust port of the engine to direct exhaust gases away from the engine. The coolant conduit is disposed in thermal communication with the exhaust conduit. The coolant conduit comprises a first coolant passage and a second coolant passage. A coolant inlet port is disposed in fluid communication with the coolant conduit to direct a flow of coolant into the first and second coolant passages. The orifice is disposed in fluid communication between the coolant inlet port and the second coolant passage. The shape of the orifice is not limiting to the present invention. Its function is to provide a flow of liquid coolant from the coolant inlet port to the second coolant passage and provide a resistance to the flow of coolant through the orifice which changes as a function of the flow of coolant through the coolant inlet port.
The orifice and the first and second coolant passages define a first coolant path from the coolant inlet port through the first coolant passage into the second coolant passage. They also define a second coolant path from the coolant inlet port through the orifice into the second coolant passage. The orifice is shaped to provide increased resistance to flow of the coolant through the orifice as a function of increased flow of coolant through the coolant inlet port. The relative flow rates of coolant through the first and second coolant passages is determined as a function of the flow rate of coolant through the coolant inlet passage.
A drain opening is disposed in fluid communication between the coolant conduit and the exhaust conduit. A coolant outlet port is connected in fluid communication with the coolant conduit for conducting the coolant away from the coolant conduit. The coolant outlet port is disposed in fluid communication between the exhaust conduit and the coolant conduit to conduct the coolant into a stream of the exhaust gases. The exhaust conduit and the coolant conduit are disposed within an exhaust elbow of the exhaust system. The coolant conduit is a coolant conducting jacket, in a preferred embodiment of the present invention, which surrounds the exhaust conduit.